Saturated linear polyesters thermally stabilized with amines



United States Patent US. Cl. 260-453 9 Claims ABSTRACT OF THE DISCLOSUREA thermal stabilized polyester composition comprising a saturated linearpolyester and a thermal stabilizer selected from the group consisting ofsecondary and tertiary aliphatic, aromatic, or mixed aliphatic-aromaticamines.

This invention relates to highly polymeric saturated linear polyesterresins that possess improved thermal stability and to a method ofproducing same.

Saturated linear polyester resins can be prepared by first carrying outa condensation reaction between a suitable dicarboxylic acid or esterthereof with a diol to form a prepolymer. The resulting prepolymer isthen polycondensed to form the desired polyester resin. When an ester ofa dicarboxylic acid is used as the starting material, it is firstreacted with a diol in the presence of a tranesterification orester-interchange catalyst by means of an esterinterchange reaction;whereas when a dicarboxylic acid is used as the starting material, it isfirst subjected to a direct esterification reaction with a diol in thepresence of what is generally called a first stage additive or etherinhibitor. In either instance, the resulting reaction product, which maybe generally described as a polyester prepolymer, is then polycondensedin the presence of a polycondensation catalyst to form a polyesterresin.

For example, in the case of the transesterification method of preparingpolyethylene terephthalate, ethylene glycol is reacted with dimethylterephthalate to form a polyester prepolymer which is comprised mainlyof bis-2- hydroxyethyl terephthalate; or in the direct esterificationmethod, ethylene glycol is reacted with terephthalic acid to form theresulting polyester prepolymer which is then polycondensed to form thedesired polyester resin.

Saturated linear polyester resins, such as polyethylene terephthalateand many others, are widely used in the pro duction of films and fibersand the like. However, it is generally known that such polyesterproducts degrade when exposed to heat for a substantial period of time.Such degradation is particularly a problem in the extrusion and spinningprocesses of the finished resins to form the above-denoted products.Additionally, the fibers produced from such resins are extensively usedin the textile field and, as a result of this application, are subjectedto rather extreme temperatures in the processes of washing, drying, andironing. Therefore, it is highly desirable that the polyester resincomposition possess as much stability at high temperatures as possible.

Therefore, it is an object of the present invention to prepare a highlypolymeric saturated linear polyester resin composition which exhibitsimproved thermal stability.

Another object of the present invention is to provide a method ofpreparing saturated linear polyester resin exhibiting such a high degreeof thermal stability.

These and other objects are accomplished in accordance with the presentinvention with a stabilized polyester composition comprising a saturatedlinear polyester containing a minor amount of a thermal stabilizerselected from the group consisting of secondary and tertiary aliphatic,aromatic, or mixed aliphatic-aromatic amines, and physical mixturesthereof. It has been found preferable that the aromatic constituentsthereof be phenyl or benzyl radicals and the aliphatic constituentsthereof be alkyl radicals containing from 4 to 18 carbon atoms.

Among the secondary and tertiary amine compounds which can be used asthermal stabilizers in the present polyester compositions are, forexample, didodecylamine, tri-n-hexylamine, triamylamine,triisoamylamine, diheptyl amine, dipentadecylamine, diphenylamine,triphenylamine, phenylbenzylamine, diphenylheptylamine,N-didodecylaniline, N-dioctylaniline, N-dihexylaniline,dioctylbenzylamine, and dipentadecyclphenylamine.

The saturated linear polyester resins used in the preparation of thesubject thermal stabilized polyester compositions can be prepared viathe conventional ester-interchange reaction or by the directesterification method.

The ester-interchange reaction is generally carried out with a molarratio of diol, such as ethylene glycol to an ester of a dicarboxylicacid, such as dimethyl terephthalate of from about 1:1 to about 15:1,respectively, but preferably from about 1.211 to about 2.6: 1. Thetransesterification or ester-interchange reaction is generally carriedout at atmospheric pressure in an inert atmosphere such as nitrogen,initially at a temperature ranging from about 250 C., but preferablybetween about C. and 200 C. in the presence of a suitabletransesterification catalyst. For example, the transesterificationcatalyst used may be lithium hydride or zinc acetate at a concentrationranging from about 0.01% to about 0.20%, based on the weight of theester of the dicarboxylic acid used in the initial reaction mixture.During the first stage of this reaction, methyl alcohol is evolved andis continuously removed by distillation. After a reaction period ofabout 1-2 hours, the temperature of the reaction mixture is raised tofrom about 200 C. to about 300 C. for approximately 1-3 hours in orderto complete the reaction, so as to form the desired polyester prepolymerand to distill any excess glycol.

In the case of the direct esterification method of preparing saturatedlinear polyester resins, the reaction is generally carried out with amolar ratio of diol, for example, ethylene glycol, with a dicarboxylicacid, such as terephthalic acid, of from about 1:1 to about 15:1, butpreferably from about 1.2:1 to about 2.6: 1. The direct esterificationstep is generally carried out at temperatures ranging from about 180-280C. in the absence of an oxygen containing atmosphere at atmospheric orelevated pressure for about 2-4 hours to form the desired polyesterprepolymer. For example, the reaction may be carried out in anatmosphere of nitrogen.

The first stage of the direct esterification method is generally carriedout in the presence of a suitable additive or butter, such astriethylamine, at a concentration ranging from about 5X10 mole to about5 10- mole of additive per mole of dicarboxylic acid in the initialreaction mixture.

Conventionally, the polycondensation step in the prep aration of thesubject polyester resins by either the transesterification method ordirect esterification method is generally accomplished by adding asuitable polycondensation catalyst to the polyester prepolymer andheating the blend thereof under reduced pressure of from about 0.5 to 20mm. of mecury while being agitated at a temperature of from about 260325C. for from 2-4 hours. For example, the polycondensation catalystssuitable for use are antimony trioxide and antimony sec-butoxide, atconcentrations ranging from about 0.01% to about 0.2%, based on theweight of the polyester prepolymer to be polycondensed.

In the practice of the present invention, it has been found that it isprefered to mix or blend the present thermal stabilizers into the moltenpolyester resin im- 3 mediately after the polycondensation step has beencompleted.

It has been found that the above-described thermal stabilizers areeffective as such in polyester resin compositions when employed inamounts ranging from about 0.01% to about 0.5%, based on the weight ofthe polyester resin. Usually, it has been found that concentrationsranging from about 0.02% to about 0.3% are preferred in most instances.However, when indicated, concentrations less or greater than the abovecan be used, but their effectiveness is generally reduced.

The following examples of several preferred embodi merits will furtherserve to illustrate the present invention, although it will beunderstood that these examples are included merely for the purpose ofillustration and are not intended to limit the scope of the presentinvention. All parts are by weight, unless otherwise indicated.

EXAMPLE I A blended mixture comprising 474 g. of terephthalic acid, 288mls. of ethylene glycol and 149 mls. of triethylamnie was charged into areaction vessel equipped with a nitrogen inlet, a Dean-Stark separatingapparatus, heating means and stirring means. The reaction mixture wasagitated and the temperature was raised to about 197 C. under a nitrogenblanket at atmospheric pressure. At about 190 C., a water triethylamineazeotropic mixture started to distill off. The azeotropic mixture wascontinuously separated by means of the Dean-Stark apparatus, and thetriethylamine recovered was continuously returned to the reactionvessel. The reaction mixture became almost clear. Then, the temperaturewas allowed to rise to about 230 C. over a one hour period to remove allthe triethylamine and any excess glycol. The prepolymer product wasallowed to cool under an atmosphere of nitrogen.

EXAMPLE II Fifty grams of the prepolymer product of Example I was mixedwith 0.02 g. of antimony sec-butoxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury while under agitation forabout 2 hours to bring about the polycondensation of the polyesterprepolymer and formation of a polyester resin. The polyester resinformed had an original intrinsic viscosity of 0.88, a degraded intrinsicviscosity of 0.69, and the percentage broken bonds was calculated as0.132.

EXAMPLE III Fifty grams of the prepolymer product of Example I was mixedwith 0.02 g. of antimony sec-butoxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury while under agitation forabout 2 hours to bring about the polycondensation of the prepolymer andformation of a polyester resin. After the polycondensation reaction hadbeen completed, 0.02 g. of didodecylamine was thoroughly stirred intothe polyester resin while still molten at atmospheric pressure, afterwhich the resin product was cooled. The resulting polyester resincomposition had an original intrinsic viscosity of 0.63, a degradedintrinsic viscosity of 0.58, and the percentage broken bonds wascalculated as 0.060.

EXAMPLE IV Fifty grams of the prepolymer product of Example I was mixedwith 0.02 g. of antimony sec.-butoxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury while under agitation forabout 2 hours to bring about the polycondensation of the prepolymer andformation of a polyester resin. After the polycondensation reaction hadbeen completed, 0.02 g. of diphenylamine was thoroughly stirred into thepolyester resin while still molten at atmospheric pressure, after whichthe resin product was cooled. The resulting polyester resin compositionhad an original intrinsic viscosity of 0.65, a degraded intrinsicviscosity of 0.59, and the percentage broken bonds was calculated as0.067.

EXAMPLE V Fifty grams of the prepolymer product of Example I was mixedwith 0.02 g. of antimony sec.-butoxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury while under agitation forabout 2 hours to bring about the polycondensation of the prepolymer andformation of a polyester resin. After the polycondensation reaction hadbeen completed, 0.02 g. of triphenylamine was thoroughly stirred intothe polyester resin while still molten at atmospheric pressure, afterwhich the resin product was cooled. The resulting polyester resincomposition had an original intrinsic viscosity of 0.67, a degradedintrinsic viscosity of 0.58, and the percentage broken bonds wascalculated as 0.092.

EXAMPLE VI Fifty grams of the prepolymer product of Example I was mixedwith 0.02 g. of antimony sec.-butoxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury while under agitation forabout 2 hours to bring about the polycondensation of the prepolymer andformation of a polyester resin. After the polycondensation reaction hadbeen completed, 0.02 cc. of tri-n-hexylamine was thoroughly stirred intothe polyester resin while still molten at atmospheric pressure, afterwhich the resin product was cooled. The resulting polyester resincomposition had an original intrinsic viscosity of 0.71, a degradedintrinsic viscosity of 0.61 and the percentage broken bonds wascalculated as 0.092.

EXAMPLE VII A mixture comprising 600 g. of dimethyl terephthalate, 396mls. of ethylene glycol, and 0.24 g. of lithium hydride was charged intoa reaction vessel equipped with a nitrogen inlet, heating means andstirring means. The reaction mixture was agitated and heated atatmospheric pressure at 198 C. under a nitrogen blanket. The reactionmixture was held at about 198 C. for about two hours, during which timeby-product methyl alcohol was distilled olf. Then, the temperature ofthe reaction mixture was allowed to rise to 230 C. over a period ofabout one hour to distill off any remaining by-product methyl alcoholand ethylene glycol and form a polyester prepolymer. The prepolymerproduct was allowed to cool under an atmosphere of nitrogen.

EXAMPLE VIII Fifty grams of the prepolymer product of Example VII wasmixed with 0.02 g. of antimony trioxide and placed in a reaction vessel.The reaction mixture was heated at about 280 C. under reduced pressureof from about 0.05 to about 0.1 mm. of mercury while under agitation forabout 3 hours to bring about the polycondensation of the polyesterprepolymer and formation of a polyester resin. The polyester resinformed had an original intrinsic viscosity of 1.13, a degraded intrinsicviscosity of 0.76, and the percentage broken bonds was calculated as0.169.

EXAMPLE IX in a reaction vessel. The reaction vessel was heated at about280 C. under reduced pressure of from about 0.05 to about 0.1 mm. ofmercury while under agitation for about 3 hours to bring about thepolycondensation of the polyester prepolymer. After the polycondensationreaction had been completed, 0.02 g. of didodecylamine was stirred intothe polyester resin while still molten at atmospheric pressure, afterwhich the resin product was cooled. The resulting polyester resincomposition had an original intrinsic viscosity of 0.86, a degradedintrinsic viscosity of 0.68, and the percentage broken bonds wascalculated at 0.122.

In the above examples, the original intrinsic viscosity values of thepolyester resin products were obtained by measuring the intrinsicviscosities of the resin compositions as produced.

The degraded intrinsic Viscosity values were determined by the followingprocedure: The polyester resin composition was ground and passed througha 10 U.S.S. mesh screen and dried at 120 C. in vacuo for 16 hours, thencooled in a desiccator. Two to three grams of this dried resin was thenplaced in a test tube which was then inserted into an aluminum blockpreheated to 280 C. (:0.5 C.). The block was then sealed and evacuatedto 0.1 mm. of mercury. After holding for about 10-15 seconds, the blockwas filled with dried, oxygen-free nitrogen gas. This vacuum-nitrogenpurge was then repeated for a total of three times; the entire processtook 5-7 minutes. Then, the resin sample was left in the heated blockfor an additional two hours under a slow stream of nitrogen. After thistwo-hour period, the resin sample was removed from the block and placedin a desiccator which was first evacuated and then filled with nitrogen.The intrinsic viscosity of the resin product was then determined andsuch an intrinsic viscosity value is noted in the examples above as thedegraded intrinsic viscosity.

The percentage broken bonds values indicated in the above examples werecalculated by the use of the following equation:

Percent Broken Bonds X 9 .6 X 10 The value of K and a may be found inthe literature, such as Conix, A., Makromol., Chemie 26, p. 226 (1958),wherein K= 0.00021 and a=0.82. V; in the above formula is the degradedor final intrinsic viscosity value and V is the original or initialintrinsic viscosity value.

All of the intrinsic viscosity determinations of the polyester resinproducts produced in the above examples were determined in a 60% phenoland 40% tetrachloroethane solution, wt./wt., at 30 0., according toconventional laboratory procedure.

The results in the above examples indicate that the present additives,when added to saturated linear polyester resins, act to stabilize orreduce the degradation effects of higher temperatures upon suchpolyester resins. The change in intrinsic viscosity or the differencebetween the original intrinsic viscosity and the degraded intrinsicviscosity is a direct measure of the heat stabilizing effect that thepresent thermal stabilizers have upon polyester resins and can bereadily calculated from the above results.

W en the controls above, Examples H and VIII, are

compared with their corresponding examples wherein the same catalystsystems were used, with the addition of a thermal stabilizer of thepresent invention, it can readily be seen from the intrinsic viscosityvalues and the percentage broken bonds values that the presentstabilizers act in all cases to limit the amount of degradation thattakes place when polyester resin products are exposed to elevatedtemperatures for prolonged periods of time.

The present invention has been illustrated with particular respect tothe stabilization of polyethylene terephthalate. However, the presentthermal stabilizers are also effective in stabilizing any saturatedlinear polyesters and copolyesters; for example, those derived fromdicarboxylic acids, such as isophthalic acid, and4,4'-diphenyldicarboxylic acid, or ester derivatives thereof, andsuitable diols, such as glycols of the series HO(CH ),,OH, where n is 2to 10.

It will be apparent that various different embodiments can be madepracticing this invention without departing from the spirit and scopethereof, and therefore, it is not intended to be limited, except asindicated in the appended claims.

We claim:

1. A stabilized polyester composition comprising a saturated linearpolyester resin having incorporated therein a minor amount of a thermalstabilizer selected from the group consisting of didodecylamine,tri-n-hexylamine, triamylamine, triisoamylamine, diheptylamine,dipentadecylamine, triphenylamine, phenylbenzylamine,diphenylheptylamine, N-didodecylaniline, N-dioctylaniline, N-dihexylaniline, dioctylbenzylamine, and dipentadecylphenylamine.

2. The composition of claim 1 wherein the polyester is polyethyleneterephthalate.

3. The composition of claim 1 containing from about 0.01 to about 0.5%by weight of a thermal stabilizer.

4. The composition of claim 1 wherein the thermal stabilizer isdidodecylamine.

5. The composition of claim 1 wherein the thermal stabilizer isdiphenylamine.

6. The composition of claim 1 wherein the thermal stabilizer istri-n-hexylamine.

7. The composition of claim 1 wherein the thermal stabilizer istriphenylamine.

8. The composition of claim 1 wherein the thermal stabilizer isphenylbenzylamine.

9. The composition of claim 1 wherein the thermal stabilizer isdiphenylheptylamine.

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HOSEA E. TAYLOR, Primary Examiner

